The majority of present day integrated circuits (ICs) are implemented by using a plurality of interconnected field effect transistors (FETs), also called metal oxide semiconductor field effect transistors (MOSFETs), or simply MOS transistors. An MOS transistor includes a gate electrode as a control electrode and spaced apart source and drain regions between which a current can flow. A control voltage applied to the gate electrode controls the flow of current through a channel between the source and drain regions.
The current carrying capability and hence the performance of an MOS transistor is proportional to the mobility (μ) of the majority carrier in the channel. The mobility of holes, the majority carrier in a P-channel MOS (PMOS) transistor, and the mobility of electrons, the majority carrier in an N-channel MOS (NMOS) transistor, can be enhanced by applying an appropriate stress to the channel. The known stress engineering methods greatly enhance circuit performance by increasing device drive current without increasing device size and device capacitance. Unfortunately, some of the known stress engineering methods work against each other; practicing one method relaxes the stress induced by another method.
Accordingly, it is desirable to provide improved methods for fabricating stress enhanced MOS transistors. In addition, it is desirable to provide methods for fabricating MOS transistors that take advantage of multiple stress engineering methods to cumulatively enhance the stress applied to the transistor channel. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.